ForHosting KIT · Developer Utilities

Series diode voltage drop calculator

This series diode voltage drop calculator adds the forward voltage of every diode in a series path, then subtracts that total from the available supply voltage.

● BetaFree · in your browser

Run — free How it works & API

Use it from WebAPIEmailTelegramApp soon

It gives you the combined diode drop, the voltage remaining for the load, and a clear indication of whether the supply is sufficient. Use individual forward-voltage values for silicon diodes, Schottky diodes, LEDs, or mixed strings so the result reflects the actual parts and operating point you intend to use.

Enter realistic forward-voltage values

Start with the DC supply voltage available at the diode string, then enter one forward-voltage value for each diode in series. Forward voltage is not a universal constant: it depends on diode chemistry, current, junction temperature, and the particular device. A small silicon signal diode may often be estimated near 0.6 to 0.7 volts, while a Schottky diode may be lower and an LED may be substantially higher. For a preliminary design, use the typical value from the component data sheet at approximately your planned current. For a conservative headroom check, repeat the calculation using the maximum specified forward voltage. Keep each diode as a separate array item when the string mixes part types or operating characteristics. The calculator preserves that list in its result, which makes the assumptions easy to review. A zero-volt entry is accepted for an idealized diode model, although a physical conducting diode normally has a positive drop. Negative, non-finite, empty, or excessively large values are rejected because they do not describe a usable forward-drop input.

Understand the total drop and remaining voltage

Diodes connected in series carry the same current, so their forward voltage drops add. The calculator performs that addition directly: total forward voltage drop equals the first diode drop plus the second, continuing through the complete list. It then computes remaining load voltage as supply voltage minus the total forward drop. For example, three drops of 0.7, 0.7, and 0.65 volts consume 2.05 volts. With a 12-volt source, 9.95 volts remain for the load under those assumptions. The result also includes the diode count and a supply-sufficient flag. If the total drop exceeds the source, the remaining voltage is negative and the flag is false. That negative number is useful: its magnitude is the voltage shortfall in the simplified model. It does not mean the physical circuit creates a negative load supply. Instead, it tells you that the assumed forward-biased operating condition cannot be maintained by the stated source. The real circuit current will fall, changing each diode's actual forward voltage.

Apply the result with appropriate engineering margins

Treat the calculation as a voltage-budget tool, not as a complete nonlinear diode simulation. The remaining voltage is the amount available to everything after the series diodes, including a resistor, regulator, transistor, battery charger, sensor, or other load. Compare it with the load's minimum operating voltage and include margin for supply tolerance, wiring loss, ripple, temperature, and component variation. When designing a reverse-polarity protection path, use the diode's forward-voltage curve at the highest expected load current and check its power dissipation separately. When sizing an LED resistor, this calculator can total the LED drops, but current still requires a resistor or regulated driver; the remaining voltage is what that current-limiting element must handle. For switching converters and linear regulators, verify that the result leaves the required input headroom or dropout allowance across the full operating range. Because the algorithm is deterministic and performs no network requests, the same inputs always produce the same rounded result. Automated API calls cost $0.002 per request, while the browser calculation can run locally for quick design checks.

What you can do with it

Budget voltage after protection diodes

Check how much supply voltage remains after one or more series diodes used for reverse-polarity or isolation protection.

Evaluate a mixed LED string

Add the individual forward drops of different LED colors before calculating the voltage that a current regulator or resistor must absorb.

Check regulator input headroom

Estimate the worst-case voltage reaching a downstream regulator after diode OR-ing, blocking, or protection components.

FAQ

How is the total series diode drop calculated?

The calculator adds every value in diode_forward_voltages. Series components carry the same path current, so their individual forward voltage drops are additive in this simplified model.

What does a negative remaining load voltage mean?

It means the assumed total forward drop is greater than the stated supply. Its magnitude is the modeled voltage shortfall; the real circuit will not sustain those assumed forward drops at that supply.

Should I use typical or maximum forward voltage?

Use typical values for a nominal estimate and maximum data-sheet values at the relevant current and temperature for a conservative headroom check. Running both reveals the likely range.

Can I mix silicon, Schottky, and LED forward drops?

Yes. Enter each device's forward voltage as a separate array item. The calculation only requires that the devices are modeled as series drops.

Does this calculate diode current or power?

No. It calculates only the voltage budget. Current depends on the rest of the circuit, and diode power is approximately forward voltage multiplied by current.

For developers — API access

Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.

API endpoint

POSThttps://api.kit.forhosting.com/elec/diode-voltage-drop

Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.

Call it from your stack

curl -X POST https://api.kit.forhosting.com/elec/diode-voltage-drop \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"supply_voltage":12,"diode_forward_voltages":[0.7,0.7,0.65]}'

const res = await fetch("https://api.kit.forhosting.com/elec/diode-voltage-drop", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.KIT_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    "supply_voltage": 12,
    "diode_forward_voltages": [
      0.7,
      0.7,
      0.65
    ]
  })
});
const { task_id } = await res.json();

import os, requests

res = requests.post(
    "https://api.kit.forhosting.com/elec/diode-voltage-drop",
    headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
    json={
    "supply_voltage": 12,
    "diode_forward_voltages": [
        0.7,
        0.7,
        0.65
    ]
},
)
task_id = res.json()["task_id"]

<?php
$res = file_get_contents("https://api.kit.forhosting.com/elec/diode-voltage-drop", false, stream_context_create([
  "http" => [
    "method"  => "POST",
    "header"  => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
    "content" => '{"supply_voltage":12,"diode_forward_voltages":[0.7,0.7,0.65]}',
  ],
]));
$task = json_decode($res, true);

body := bytes.NewBufferString(`{"supply_voltage":12,"diode_forward_voltages":[0.7,0.7,0.65]}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/elec/diode-voltage-drop", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)

Example request

{
  "supply_voltage": 12,
  "diode_forward_voltages": [
    0.7,
    0.7,
    0.65
  ]
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "elec.diode_voltage_drop",
  "status": "queued",
  "_links": {
    "result": "/tasks/tsk_…/result"
  }
}

The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.

Pricing

Per request$0.002

Published price — no tokens, no invented credits. A failed task is never charged.

Limits

`max_diodes`	1000
`max_voltage`	1000000000

Errors

HTTP	Code	Meaning
`401`	`unauthorized`	Missing or invalid API key.
`402`	`insufficient_balance`	Your balance doesn't cover the task price.
`404`	`unknown_type`	That task type doesn't exist.
`429`	`rate_limited`	Too many requests. Use the webhook instead of polling.

Read the full KIT documentation →