Making a sigma-delta ADC for controlling a

panel heaterKenji Yamamoto

Sensible analog circuit lab.

Sometimes we want to design a controller for a panel heater

PWM?

Designing the circuit with analog components would be difficult.

Continuous voltage control?

The power dissipation would not be acceptable.

Sigma delta?

You may not know how to design it.

But it is easy to implement at very low cost.

You may not know how to calculate the value of the components, but can find the appropriate values with simulations.

The circuit

V2

5

GND

TRIG

OUT

RST CV

THRS

DIS

VCC

U3

TLC555

R81meg

C5

1u

R11

100k

R12

1megC1

1u

R2

100k

V1

SINE(0 2.5 0.02)

U4

C3

0.01u

R110k

R310k

C4

0.1u

U2U5R4

10k

R5

10k

R6

1 C2

0.1u

C6

0.1u

VDD

VDD

SDOUT

VCON

VC

VDD

V2

VFB

VFB

VDD

VDD

HVDD

HVDD

2

HVDD VD

D

VDD

HVDD

2

HVDD

2

BVCVI

.tran 1000

.IC V(SDOUT)=2.5

.ic V(VC)=2.5

*.options cshunt=1e-15*.options gshunt=1e-9

.include ./NJM2902OPAMP/njm2902_2.lib

A sigma-delta implementation with a TLC555

Output filter

SDOUT is a smoothed voltage of the ADC output.

LM2902LM2902

Z of PS

Bypass caps

LM2902

Features:Low costFor relatively slow signals

Performance

0s 10s 20s 30s 40s 50s 60s 70s 80s 90s 100s0.0V

0.5V

1.0V

1.5V

2.0V

2.5V

3.0V

3.5V

4.0V

4.5V

5.0V0.0V

0.5V

1.0V

1.5V

2.0V

2.5V

3.0V

3.5V

4.0V

4.5V

5.0V-0.5V

0.0V

0.5V

1.0V

1.5V

2.0V

2.5V

3.0V

3.5V

4.0V

4.5V

5.0V

V(vfb)

V(sdout)

V(vi)

Input waveform

SDOUT, smoothed output waveform

Sigma-delta ADC output waveform

Frequency domain waveform of SDOUT

Conclusion

You can control a panel heater with a solid state relay connected to a sigma-delta ADC. The VFB signal can be used to control the solid state relay.

You can apply an analog voltage, which can be set with a variable resistor, on the ADC’s input to control the power of the panel heater.

Hoping that you will have good luck with your home project!

If you want the data deck of the circuit, send a request to yamaken@erqii.com