# Thyristor phase-controlled rectifier

Canonical URL: https://eloragrid.ai/symbols/thyristor-phase-controlled-rectifier
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: SCR REC
Drawing use: SLD, Schematic
Reference families: IEC, IEEE / ANSI

An AC-to-DC converter using thyristors fired at a controlled angle to set its DC output voltage.

## In plain English

### What does Thyristor phase-controlled rectifier mean?

A phase-controlled rectifier uses thyristors instead of diodes, so the firing angle sets the average DC output voltage. Six-pulse bridges are widely used for large battery chargers, electrolysers, DC drives and older UPS rectifiers because they are robust and simple to control.

### A simple example

On single-line diagrams it appears as the rectifier box with AC and DC marks plus a thyristor or control additional drawing mark, or as a bridge of thyristor symbols on detailed schematics. A rectifier transformer, line reactor and harmonic filter are often drawn upstream.

### What the drawings help you do

Reducing the output voltage by delaying firing also lowers the input power factor, and the converter draws characteristic harmonics at 5th, 7th, 11th and 13th orders. The symbol does not show these effects, which must be assessed with the network harmonic study.

### This particular reference

An AC-to-DC converter using thyristors fired at a controlled angle to set its DC output voltage. A phase-controlled rectifier sets voltage by firing angle; an active front-end rectifier uses switched transistors and can run near unity power factor.

### Terms

- DC: Direct current: electricity flowing in one direction.
- AC: Alternating current: electricity whose direction changes periodically.
- Winding: A coil of conductor inside an electrical machine or transformer.

Concept diagram: Identify the device and form → Read the connections and state → Check the equipment reference
A guide to reading this reference. The original symbol illustration and its drawing notes appear below; these boxes are not a wiring diagram.

- [AutoCAD Electrical: Semiconductor components](https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-AC954072-7314-4682-88AF-38160D61E9A2.htm)
- [IEC graphical symbols for diagrams](https://tc3.iec.ch/tc-activity/graphical-symbols-for-diagrams/)


## What it represents

A phase-controlled rectifier uses thyristors instead of diodes, so the firing angle sets the average DC output voltage. Six-pulse bridges are widely used for large battery chargers, electrolysers, DC drives and older UPS rectifiers because they are robust and simple to control.
On single-line diagrams it appears as the rectifier box with AC and DC marks plus a thyristor or control qualifier, or as a bridge of thyristor symbols on detailed schematics. A rectifier transformer, line reactor and harmonic filter are often drawn upstream.
Reducing the output voltage by delaying firing also lowers the input power factor, and the converter draws characteristic harmonics at 5th, 7th, 11th and 13th orders. The symbol does not show these effects, which must be assessed with the network harmonic study.

## How to read it

- A thyristor mark inside or beside the rectifier block distinguishes it from a diode rectifier.
- Expect harmonic filtering or a phase-shifting transformer on large units.

## Information to show or reference

- State pulse number and DC rating.
- Show rectifier transformer and line reactor.
- Reference harmonic study and filter design.

## Important distinction

A phase-controlled rectifier sets voltage by firing angle; an active front-end rectifier uses switched transistors and can run near unity power factor.

## Facts

- Switching device: Thyristor
- Control: Firing angle
- Characteristic harmonics: 6k plus or minus 1 for a six-pulse bridge
- Preview: Independent educational illustration; consult the applicable standard and project legend for the exact graphic

## Public references

- [AutoCAD Electrical: Semiconductor components](https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-AC954072-7314-4682-88AF-38160D61E9A2.htm) — Autodesk. Public semiconductor symbol family including thyristor forms.
- [IEC graphical symbols for diagrams](https://tc3.iec.ch/tc-activity/graphical-symbols-for-diagrams/) — IEC. IEC graphical symbol context for converters.

## Graphic scope

Independent original educational concept illustration by Elora Grid. Not a certified standards graphic or manufacturer footprint. Unitless; not to scale. Original artwork licence: https://creativecommons.org/licenses/by/4.0/. Publisher material is linked only.