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Mini Switching Power Supply 5V - 25V, 3A with TNY268 and PCB |
- PWM Control, Power Mosfets
- Overcurrent Protection
- Over-Temperature Protection
- Self-Feeding System
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Technical Specifications
Design
Caution!
Features
TNY268 - Pinout and Description
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Fig. 2 - Pinout - Pinout TNY268 |
We leave below the description of each pin of the TNY268 Integrated Circuit to facilitate our understanding.
- DRAIN (D): Power MOSFET drain connection. Provides internal operating current for start-up and steady-state operation.
- BYPASS (BP): Connection point for an external 0.1 µF bypass capacitor for the internally generated 5.8 V supply.
- ENABLE/UNDERVOLTAGE (EN/UV): This pin has two functions: input enable and line undervoltage detection. During normal operation, power MOSFET switching is controlled by this pin. MOSFET switching is terminated when a current greater than 240 μA is drawn from this pin.
This pin also detects line undervoltage conditions through an external resistor connected to the DC line voltage. If there is no external resistor connected to this pin, TinySwitch-II detects its absence and disables the line undervoltage function. - SOURCE (S): Common control circuit, connected internally to the output MOSFET source.
- SOURCE (HV RTN): MOSFET source connection output for high voltage feedback.
The Switched Power Supply Circuit
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Fig. 3 - Schematic Diagram Mini Switching Power Supply 5V - 25V, 3A with TNY268 |
Regulate The Output Voltage
The output voltage is adjusted through two parameters in the circuit:
- The D4 diode, which is a 1W Power Zener diode.
- The secondary winding of the transformer.
The Zener Diode
For example:
The Transformer
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Fig. 4 EE-25 Ferrite Transformer |
Primary coil winding
Secondary coil winding
The calculation for an output voltage of 5V can be achieved using the formula below:
- N = Number of Turns
- V = Desired Voltage
- C = Constant = 1.4
- V = 5V
- C = 1.4
- N = ?
- N = 5 * 1.4
- N = 7 laps
The calculation for an output voltage of 9V:
- V = 9V
- F = 1.4
- N = ?
- N = 9 * 1.4
- N = 12.6 = ~13 Rounds
The calculation for an output voltage of 12V:
- V = 12V
- F = 1.4
- N = ?
- N = 12 * 1.4
- N = 16.8 = ~17 Rounds
The calculation for an output voltage of 24V:
- V = 25V
- F = 1.4
- N = ?
- N = 25 * 1.4
- N = 35 Turns
For 24V output, we have 37 turns to wind in the secondary.
Components list
Semiconductor
- U1 ......... Integrated Circuit TNY268P
- OPT....... TLP181 Opto-Coupler
- D1, D2 ... Diode 1N4007
- D3 ......... Fast Diode FR307
- D4 ......... Zener Diode *See Text
Resistor
- R1 .... Resistor 10Ω / 1W (brown, black, black, gold)
- R2 .... Resistor 200KΩ / 1/4W (red, black, yellow, gold)
- R3 .... Resistor 470Ω / 1/4W (yellow, violet, brown, gold)
Capacitors
- C1 ....... Electrolytic Capacitor 47uF/400V
- C2 ....... Polyester Capacitor 2.2nF
- C3 ....... Polyester Capacitor 100nF
- C4 ....... Electrolytic Capacitor 470uF/35V
Several
- T1 ......... EE-25 Ferrite Transformer
- P1, P2 ... Connector WJ2EDGVC-5.08-2P
- Others... PCI, Wires, Solders, Etc.