TL494 general multipurpose power inverter driver circuit (half bridge)

 TL494 general multipurpose power inverter driver circuit

TL494 general multipurpose power inverter driver circuit

Ever notice how many projects use the same sort of oscillator: be it gate drivers, or half-bridge setups? If not, flybacks, induction heaters and Solid State Tesla Coils are what I'm thinking of. Since they can all use the same basic driver why not make one universal driver to use for all these projects? Fueled by this thought I made a TL494 based oscillator which has separate pulse width and frequency control. This then runs a simple gate driver stage and finally a half-bridge. To ensure that I could keep Mosfet deaths to a minimum I put some safety features in place. First a primary current detection transformer is used to monitor the current through the load, and shut down the inverter if some threshold is reached. Second a thermistor is placed directly on one of the Mosfets to monitor their current temperature, again once a threshold is reached the inverter is shut down. This eliminated two major causes of catastrophic failure, though that's not to say things don't still go wrong. I now use my multi-inverter for both projects whenever I need a quick demonstration.

The TL494 part is pretty straight-forward, pretty much just taken from a datasheet. The internal comparators are in parallel and set up as voltage followers. The voltage at pin 1/16 (non-inverting inputs) is varied between 0,6 and 3,0V using a potentiometer and some resistors. This alters the duty cycle from maximum to a predetermined "safe" minimum based on the sharpness of the switching waveforms. The discrete gate driver is a full-bridge, allowing the use of 1:1:1 Gate Drive Transformers (GDTs). It shorts the core during dead-time, which effectively shorts the gates of the mosfets preventing spurious drive signals. The CT part of the circuit is simple analog circuitry. If voltage through a transformer is stepped up, current is stepped down, so if 14A are flowing through the current transformer's primary, and it has a ratio of 1:35, the current is 400 mA. Knowing Ohm's law, this implies that the voltage over the burden resistor must be U= R*I, so 6,8Ω * 0,4A = 2,72 V. The rectifying diode steals about 0,13 volts (measured) from this, resulting in 2,59V at the comparator. With the voltage divider on the other input set to 3V this means the over current latch would still be roughly 0,4V (2A) from triggering. Don't bring the reference value over 3,5V, or the shutdown state won't latch! Blame the LM324 for this... The reason 16A is selected despite the 14A rating of IRFP450s is due to the anticipated current waveform the inverter will be switching. The average value of the current should remain well under 14A in most conditions. An idea for future iterations would be an external current limit potentiometer. The thermistor section is just a couple of voltage dividers and comparator. The resistor values were found by heating the thermistor while on a heatsink, until it was deemed hot enough. The resulting thermistor resistance was roughly 3,3k.

TL494 general multipurpose power inverter driver PCB

TL494 Current-Mode PWM Controller IC Explained: Pinout, Equivalent, Sample Circuits, Applications, Features 

TL494 PWM IC Pinout DIP Package electrobuff.blogspot.com

 

TL494 Current-Mode PWM Controller
TL494 Pinout

The TL494 IC is a fixed frequency current-mode PWM controller IC with all the functions that are required in the construction of the pulse-width modulation (PWM) control circuit on a single chip.

 

TL3843 Pinout Configuration

Pin Number	Pin Name	Description
1	1IN+	Noninverting input to error amplifier 1
2	1IN-	Inverting input to error amplifier 1
3	FEEDBACK	Input pin for feedback
4	DTC	Dead-time control comparator input
5	CT	Capacitor terminal used to set the oscillator frequency
6	RT	Resistor terminal used to set the oscillator frequency
7	GND	Ground Pin
8	C1	The collector terminal of BJT output 1
9	E1	The emitter terminal of BJT output 1
10	E2	The emitter terminal of BJT output 2
11	C2	The collector terminal of BJT output 2
12	VCC	Positive Supply
13	OUTPUT CTRL	Selects single-ended/parallel output or push-pull operation
14	REF	The 5-V reference regulator output
15	2IN-	Inverting input to error amplifier 2
16	2IN+	Noninverting input to error amplifier 2

TL494 Specifications & Features

• Supply Voltage: 7V to 40V
• Number of Outputs: 2 Output
• Switching Frequency: 300 kHz
• Duty Cycle - Max: 45 %
• Output Voltage: 40 V
• Output Current: 200 mA
• Fall Time: 40 ns
• Rise Time: 100 ns
• Available in 16-pin PDIP, TSSOP, SOIC and SOP Packages

 

Equivalent/Substitute for TL494: UC3843, TL3842

Alternatives PWM controller IC:  UC2842, SG2524

 

Where to use the TL494 PWM Controller IC

The TL494 fixed frequency PWM Controller can be used for DC to DC conversion regardless of buck or boost topology. TL494 can be used to provide a constant current by varying the output voltage to the load. This IC feature an output control circuit, a flip flop, a dead time comparator, two different error amplifiers, a 5V reference voltage, an oscillator, and a PWM comparator.

So if you are looking for an IC to produce PWM signals for controlling a power switch based on the current flowing through the circuit, then this IC might be the right choice for you.

 

How to use TL494 IC

A test circuit from the TL494 datasheet is shown below.

TL494 PWM IC Circuit Application and Pinout electrobuff.blogspot.com

Non inverting pins are connected to the Ref pin while inverting pins are connected to the ground. Test inputs are given to DTC and FEEDBACK pins. External capacitor and resistor are connected to pin 5 & 6 to control the oscillator frequency. The error amplifier compares a sample of the 5-V output to the reference and adjusts the PWM to maintain a constant output current

 

Applications of TL494

• Desktop PCs
• Microwave Ovens
• Server PSUs
• Solar Micro-Inverters
• Washing Machines: Low-End and High-End
• E-Bikes
• Power: Telecom/Server AC/DC Supplies:
• Smoke Detectors
• Solar Power Inverters

 

2D-Model of TL494

Dimensions for TL3494 IC is given below. These dimensions are for the PDSO package. If you are using a different package IC, please refer to the TL494 datasheet.

TL494-Dimensions 2D PCB Footprint  electrobuff.blogspot.com

youtube.com/@ELECTROBUFF